MotionMotion

Speed, velocitySpeed, velocity

Acceleration, & MomentumAcceleration, & Momentum

MotionMotion

An object is in motion when its An object is in motion when its distance from another object is distance from another object is changingchanging

We use a reference point to We use a reference point to determine if an object is in motiondetermine if an object is in motion

When studying motion, we can When studying motion, we can calculate speed, velocity, calculate speed, velocity, acceleration, & momentum acceleration, & momentum

Frames of ReferenceFrames of Reference

Object or point from which motion is Object or point from which motion is determineddetermined

Most common frame Most common frame of reference is the of reference is the

EarthEarth Motion is a changeMotion is a change

in in positionposition relativerelative to to

a frame of referencea frame of reference

Understanding MotionUnderstanding Motion If you are on a ferry boat, how can you determine If you are on a ferry boat, how can you determine

if it is in motion?if it is in motion? If the ferry boat is moving, are you in motion?If the ferry boat is moving, are you in motion?

Are you in motion relativeAre you in motion relativeto the people around you? to the people around you? (the people are the (the people are the Reference point.)Reference point.)

Are you in motion relativeAre you in motion relativeto the trees on shore?to the trees on shore?(the trees are the reference(the trees are the referencepoint)point)

If you are standing still and If you are standing still and your friend walks by, who is in your friend walks by, who is in

motion?motion? Answer: You are moving relative to your friend, Answer: You are moving relative to your friend,

and your friend is moving relative to you! You are and your friend is moving relative to you! You are both in motion.both in motion.

You are not moving relative to the Earth, but your You are not moving relative to the Earth, but your friend is. You are both moving relative to the friend is. You are both moving relative to the sun! It depends on the frame of reference used.sun! It depends on the frame of reference used.

What is motion?What is motion?

If you and your friend are walking down the hall If you and your friend are walking down the hall together at the same speed, in the same direction, together at the same speed, in the same direction, are you moving relative to your friend?are you moving relative to your friend? Is your friend moving relative Is your friend moving relative

to you?to you? Are either of you moving Are either of you moving

relative to the Earth?relative to the Earth?

Answer:Answer: You are NOT moving relative to your friend, and your You are NOT moving relative to your friend, and your

friend is NOT moving relative to you. You both are friend is NOT moving relative to you. You both are moving relative to the Earth.moving relative to the Earth.

When studying motion, the frame of reference must When studying motion, the frame of reference must always be considered.always be considered.

SpeedSpeed

Speed = Distance ÷ TimeSpeed = Distance ÷ Time

D_ D_

S TS T

Example: A car travels 300km in 6 Example: A car travels 300km in 6 hours. What is the speed of the car?hours. What is the speed of the car?

Answer:Answer:

Speed = distance ÷ timeSpeed = distance ÷ time Speed = 300km ÷ 6 hoursSpeed = 300km ÷ 6 hours Speed = 50km/hrSpeed = 50km/hr

More practiceMore practice

1. How far can a plane travel if it flies 1. How far can a plane travel if it flies 800km/hr for 9 hours?800km/hr for 9 hours?

2. How long does it take a ship to go 500 2. How long does it take a ship to go 500 km if it travels at a speed of 50km/hr?km if it travels at a speed of 50km/hr?

AnswerAnswer

1. 1. DD SS T T

DD800800 9 9

800km 800km ▪ 9hrs = 7200km ▪ 9hrs = 7200km hrhr

AnswerAnswer

2. 2. DD SS T T 500 500 5050 T T

500km ÷ 500km ÷ 50km50km = 10 hrs = 10 hrs hrhr

VelocityVelocity Speed in a given direction.Speed in a given direction.

What is the velocity of a boat that What is the velocity of a boat that travels from St. Peter to Mankato travels from St. Peter to Mankato (10 miles) in 15 minutes?(10 miles) in 15 minutes?

2 cars are traveling 32 miles per hour, but one is going North, the other is going South.

Do they have the same speed?Do they have the same velocity?

AnswerAnswer

Speed = distance ÷ timeSpeed = distance ÷ time Speed = 10 miles ÷ 15 Speed = 10 miles ÷ 15

minutesminutes Speed = 0.67 mi/minSpeed = 0.67 mi/min Velocity = 0.67 mi/min SouthVelocity = 0.67 mi/min South

What is the difference between What is the difference between speed and velocity?speed and velocity?

Answer: velocity includes a directionAnswer: velocity includes a direction

How long does it take an 8How long does it take an 8thth grader to grader to get from Mrs. McLaren’s classroom get from Mrs. McLaren’s classroom door to Mrs. Peterek’s classroom door?door to Mrs. Peterek’s classroom door?

How would we solve this? How would we solve this?

Answer:Answer:

1. We’d need to measure the speed of an 1. We’d need to measure the speed of an average 8average 8thth grader grader

2. We’d need to measure the distance from 2. We’d need to measure the distance from Mrs. McLaren’s door to Mrs. Peterek’s doorMrs. McLaren’s door to Mrs. Peterek’s door

3. We’d need to calculate time, when we 3. We’d need to calculate time, when we know the speed and the distance. know the speed and the distance.

Time = distance/speedTime = distance/speed

Distance-time graphsDistance-time graphs

On your paper, graph the following:On your paper, graph the following: D (m)D (m) T (sec) T (sec)

00 00 55 77 1010 14 14 1515 21 21

Was your graph a straight Was your graph a straight line?line?

A A distance-time graphdistance-time graph which is which is a a straight linestraight line indicates indicates constant speedconstant speed..

In constant speed, the object In constant speed, the object does not speed up or slow does not speed up or slow down. (The acceleration is down. (The acceleration is zero.)zero.)

Graph the following on a Graph the following on a distance-time graph:distance-time graph:

D (m)D (m) T (s)T (s) 00 00 55 11 2020 224545 338080 44125125 55

0 1 2 3 4 5

Was your graph a curve?Was your graph a curve?

A graph that A graph that curvescurves on a on a distance-time graphdistance-time graph shows shows that the object does not have that the object does not have a constant speed.a constant speed.

Distance-time graphsDistance-time graphs

Describe the motion of the object as Describe the motion of the object as shown in the shown in the

graph.graph.From 0-8 sec, constant speed:(25 m/sec);From 8-12 sec, no motion;From 12-16 sec, acceleration;From 16-20 sec, constant speed

AccelerationAcceleration Acceleration is the rate at which

velocity changes

Can be change in speed or direction If an object is speeding up, it is said to have

a positive acceleration If an object is slowing down, it is said to

have a negative acceleration If an object changes direction, but maintains

a constant speed, it is still accelerating

Acceleration = change in velocity (Vf-Vi)

change in time

Acceleration problemAcceleration problem

A roller coaster’s A roller coaster’s velocity at the top velocity at the top of a hill is 10m/s. of a hill is 10m/s. Two seconds later it Two seconds later it reaches the bottom reaches the bottom of the hill with a of the hill with a velocity of 26m/s. velocity of 26m/s. What is the What is the acceleration of the acceleration of the roller coaster?roller coaster?

Answer:Answer:

Acceleration = Acceleration = change in velocity change in velocity (Vf-Vi) divided by (Vf-Vi) divided by change in timechange in time

a = a = 26 m/s – 10 m/s26 m/s – 10 m/s2 s2 s

a = a = 16 m/s16 m/s2 s2 s

a = 8 m/s/s or 8 m/sa = 8 m/s/s or 8 m/s22

Enough of an acceleration to make Matthew’s face look like this:

What do the following speed-What do the following speed-time graphs depict?time graphs depict?

More acceleration problemsMore acceleration problems

1. A car traveling at 80 mi/hr slows down 1. A car traveling at 80 mi/hr slows down to 60 mi/hr for a speed limit sign. If it takes to 60 mi/hr for a speed limit sign. If it takes them 5 seconds to slow down, what was them 5 seconds to slow down, what was the car’s acceleration? the car’s acceleration?

2. A car travels at 60 miles per hour 2. A car travels at 60 miles per hour around a curve. Is the car accelerating?around a curve. Is the car accelerating?

3. A car travels in a straight line at 3. A car travels in a straight line at 60mi/hr. Is the car accelerating?60mi/hr. Is the car accelerating?

Answers:Answers:

1. 1. a=a= vf-vi vf-vi tt

a= a= 80 mi/hr – 60 mi/hr80 mi/hr – 60 mi/hr 5 s5 s

a = 4 mi/hr/sa = 4 mi/hr/s2. Yes! Because it’s changing direction!2. Yes! Because it’s changing direction!3. No! It’s not changing speed or direction!3. No! It’s not changing speed or direction!

DecelerationDeceleration

Negative accelerationNegative acceleration Example: A car slows from Example: A car slows from

60mi/hr to 20mi/hr in 4 60mi/hr to 20mi/hr in 4 seconds. What is its seconds. What is its acceleration?acceleration?

Answer:Answer: Acceleration = change in velocity/change in Acceleration = change in velocity/change in

timetime Acceleration = Acceleration = Vf – ViVf – Vi

tt a = a = 20mi/hr – 60mi/hr20mi/hr – 60mi/hr

4 s4 sa = a = -40mi/hr-40mi/hr

4s4sa = -10mi/hr/sa = -10mi/hr/s

Review:Speed-time graph of Review:Speed-time graph of accelerationacceleration

Review: Speed-time graph of Review: Speed-time graph of decelerationdeceleration

Review: Distance-time graph of Review: Distance-time graph of constant speedconstant speed

MomentumMomentum

Momentum = Mass x Momentum = Mass x VelocityVelocity

Which has more Which has more momentum: a 300lb football momentum: a 300lb football player moving at 5m/s or a player moving at 5m/s or a 200lb quarterback moving 200lb quarterback moving at 10m/s?at 10m/s?

Answer:Answer:

Momentum of the 300lb player isMomentum of the 300lb player is300lbs x 5m/s = 1500lb-m/s300lbs x 5m/s = 1500lb-m/s

Momentum of the quarterback isMomentum of the quarterback is 200lbs x 10m/s = 2000lb-m/s200lbs x 10m/s = 2000lb-m/s

The quarterback has a greater The quarterback has a greater momentum!momentum!